Traditional 2G and 3G networks consist of one data stream, single input/single output (“SISO”) systems. Other networks, including, without limitation, Long Term Evolution (“LTE”) networks, utilize a MIMO system. They utilize two streams of data operating on the same channel. They rely on multipath effects to allow the network to disseminate the two streams of data independently to increase download and upload speeds. It is conventional wisdom in the signal processing community that repeaters do not work in these MIMO networks.
As shown in FIG. 1, a repeater 01 with one donor antenna 02 does not work for a base station 04 using antennas 05, 06 to send MIMO signals 07, 08 because of the “keyhole effect.” Because both signals 07, 08 must go through a “keyhole,” i.e., the one donor antenna 02, all MIMO benefits are lost. The network only operates at SISO speeds.
Alternatively, a MIMO network might use a dual repeater with two donor antennas. However, as shown in FIG. 2, if there is a clear line of sight between the dual repeater 01 with two donor antennas 02, 03, and the base station 04 using antennas 05, 06 to send MIMO signals 07, 08, there is only one effective path, not two. Consequently, all MIMO benefits are lost.
As shown in FIG. 3, if there is scattering of one 07 of the signals 07, 08, two paths are maintained. However, in such a network, if the condition number, the ratio of the strongest signal 08 to the weakest 07 of the two MIMO signals 07, 08 expressed in decibels (“dB”) must be low or a high signal to noise ratio (“SNR”) is required.
The present invention utilizes two orthogonally polarized antennas on the base station to transmit two orthogonally polarized MIMO signals to two orthogonally polarized donor antennas on two repeaters to maintain two paths. It also utilizes a mechanism to restore high orthogonality in the two orthogonally polarized signals.